During pressure measurement in a container, normally a pressure gauge is connected to the container by means of a conduit, a so-called impulse conduit. The impulse conduit, through which the pressure is conveyed from the container to the pressure gauge, is often long and normally has a small inner cross section area. When the pressure medium, which may be in gaseous or liquid state, is mixed with solid material, for example dust or sludge, there is a constant risk that solid material enters the impulse conduit and remains there, resulting in clogging or other disturbance. The risk of this increases when there are pressure variations or pressure impulses in the container or if there is a leakage in the impulse conduit or the pressure gauge.
To prevent the risk of clogging, filters or traps are installed, which often function unsatisfactorily. This is particularly the case when the pressure medium is in great motion or has a high temperature. Another solution is continuous or regular flushing of the impulse conduit. In that connection a clean pressure medium is used, which may be supplied to the impulse conduit from a special system or, as in SE 8206195-3, from the same pressure source as the pressure medium in the container but taken out clean at a suitable location in the plant and supplied to the impulse conduit.
In the latter case the purging flow is determined by the pressure difference between that point where the clean pressure medium is taken out and the measuring point. In other cases the purging flow is maximized by measurement or process aspects. From the point of view of process technique, the disturbance from a purging flow may be sensitive, especially in conveying pipes where a particulate, solid material is transported at great speed. Too large inflows through the measuring outlet disturb the flow in the conveying pipe, resulting in greatly increased erosion on the conveying pipe.
Considering the limitations on the purging flow, conditioned by process or measurement aspects, the risk remains, using the state of the art, that solid material will enter the impulse conduit. This also means that the risk of clogging or disturbance of the measurement remains, especially in systems with great pressure variations or when leaks (even small ones) occur in the impulse conduit or the pressure gauge.